When foods are stored in food business such as restaurants and food shops, and in the general home, and further, when foods are heated in microwave ovens, thin thermoplastic resin films have hitherto been used. Of these, food packaging wrap films of the vinylidene chloride copolymer resin family combine excellent properties such as moisture resistance, oxygen gas barrier properties, heat resistance, adhesion to containers, etc. and transparency, so that they are in heavy usage as food packaging wrap films.
Further, in recent years, food packaging wrap films comprising non-chlorine resins have also variously been proposed. For example, there are ones mainly comprising polyolefin resins such as a polyethylene resin, a polypropylene resin and a 4-methylpentene resin. The polyolefin resins such as the polypropylene resin are poor in gas barrier properties, and adhesion on surfaces of the films is also scarcely observed, so that adhesion performance indispensable as the food packaging wrap films is insufficient. In order to satisfy such desired performance, a great number of films have been proposed to which various additives are added, in which other resins are contained, or on which other resin layers are provided.
These films have been designed to improve adhesion to containers, heat resistance, etc. depending on the kind of resin used, the kind and amount of additive used together, the kind of resin used for lamination, etc. However, they have been inferior to the above-mentioned wrap films of the vinylidene chloride copolymer resin family in terms of gas barrier properties and adhesion to containers. Then, as techniques considering gas barrier properties of the wrap films mainly comprising non-chlorine resins, there are JP-A-6-322194 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”), JP-A-6-155677, JP-A-7-3089, etc. However, none of them provide satisfactory films.
For example, in JP-A-6-322194, produced is a film having as a surface layer a resin composition in which a flexible styrene-ethylene-butylene-styrene block copolymer and liquid polybutene for imparting adhesion are mixed with a propylene resin. However, the liquid polybutene is a liquid, so that mixing thereof with the polyolefin resin results in softening of the film to cause loss of anti-drape stiffness and stiffness. Accordingly, when the film is cut, it becomes easy to cling to fingers or goods to be packaged, resulting in unavailability thereof as a packaging film.
Further, JP-A-6-155677 produces a film comprising an ethylene-vinyl alcohol layer having provided on both sides thereof adhesion imparting agent-containing polyolefin resin layers on contact with acid-modified polyolefin layers, and considers easiness of cutting as well as gas barrier properties. However, this pursues good cutting properties, so that no softening agent is contained in the film. The film is therefore rather hard, and there is further room for improvement in terms of film flexibility such as good touch and followability to the shape of goods to be packaged.
JP-A-7-3089 provides a monolayer or multilayer film comprising a resin composition further containing a polyolefin resin graft-modified with an unsaturated carboxylic acid or a derivative thereof, in addition to the composition of JP-A-6-322194. In this technique, the problems of the softened film and difficulty in handling at the time when the film is cut have also been left.
An object of the invention is to provide a non-chlorine resin film useful as a packaging film, which is improved in gas barrier properties and adhesion even when a polypropylene resin poor in gas barrier properties and adhesion is used, and further takes ease of use into account, in order to solve such problems.